Oral Design Qld | Engineering Meets Aesthetics-Part 2

3 4 - e L A B O R A T E N o v e m b e r / D e c e m b e r 2 0 0 5 D evelopment of a new concept ceramic is a tall order in a day where just about everybody has their own unique system. Using the natural tooth as a model, Heraeus Kulzer (HK) set about reverse engineering a tooth and identified some of nature’s building blocks; they call this technique “Gradient Engineered Ceramics”. With the aid of the world’s most sophisticated production facility for quartz glass, they created a frit that closely resembles natural enamel and dentine (Figure 1). With the basic components closely resembling nature in opalescence and fluorescence, it then became the job of experienced master ceramists to help HK to fine tune this raw material into a cer amic that was both easy to use and able to pro- duce truly realistic crowns. Paul Feichter (Figure 2) was instrumental in this endeavour and designed a system called the Matrix. With this kit, in addition to the normal dentine and incisal kit, those of us who like to experiment with techniques and materials are able to let our hair down. As I said in the previous instalment, Heraceram has the great ability to interact with the “Dance of Light” and enable us to create natural effects in crowns without a great deal of effort. However, as we know, every tooth is different and identifying the differences and then translating that to our ceramic has been the goal of every techni- cian. To successfully use the Heraceram Matrix kit we need to look at a tooth from a different perspective (Figure 3). As always, one of the first and most important factors to be identified in a tooth is the Value. It has been shown in many circumstances that if the value is correct, then even slight mistakes in hue and chroma can be disguised, because the crown will blend in better (Figure 4). The problem we often encounter is that what we see in the lab and in the surgery are often different from what is seen in natural daylight (Figures 5a and 5b). The light sources we use in the surgery and lab do need to be the correct colour temperature and saturation, but even when we go to great lengths to match the lights we still often encounter inconsistencies. I believe the cause of this phenomenon is ultra violet light. Many surgeries and labs have exposure to natural day light but the amount can vary during different times of the day, or can be influenced by weather and atmospheric conditions eg. smoke haze or pollution. As a consequence, there has been a tendency to ignore daylight in the equation when we take a shade, by on ly using artificial light or new age digital shade taking machines. The amount of natural visible daylight probably should be ignored, due to the variations mentioned, but the influence of ultra violet light on the fluorescence and thus the value is often also overlooked (Figures 6a and 6b). The ultra violet light spectrum is usually excluded from most fluorescent light tubes (otherwise we would get sunburnt inside). The absence of this part of the spectrum can cause the incorrect identification of the tooth’s value range. I’m not suggesting that we rush out and install UV lights in our offices (or mirror balls!), but we need to look at fluorescence and value in the presence of some source of UV, preferably diffused daylight. Remember the amount of visible daylight is not so important, just some light that contains UV. Back to Heraceram: the system has been designed very much to take UV and fluroescence into account. Firstly , we have fluroesence provided at the opaque layer, where it should be, since in natural teeth the fluorescence is manifest in the pulp and dentine (Figure 7). Secondly, to account for those teeth with varied fluorescence and brighter areas, they have developed the Value pow- ders. These are supplied to correlate loosely to the Vita Classic shade guide. Engineering meets aesthetics - Part 2 BY RA Y SHARKEY, RDT TECHNIQUES Figure 1. A Heraceram frit Figure 2. Paul F eichter ZTM. Figure 3. The subtle influence o f V alue, Tra nslucency and Chroma can be seen in this example of natural aesthetics. (Paul Feichter ZTM).

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Oral Design Qld | Engineering Meets Aesthetics-Part 2